Modern naval vessels require electrical coupling and common grounding of all on-board metal structures and equipment to prevent inductive pickup of electrical signals and resulting generation of electromagnetic interference in critically important communications and other signal generating and receiving apparatus. When shipboard components cannot be integrally or metallurgically joined to other structures, coupling is typically accomplished through the use of metal straps sometimes referred to as bonding straps, most frequently constructed of copper cable with either stainless steel or aluminum end fittings, depending on the types of metals being bonded. Frequently, the bonding straps are used to couple components constructed of galvanically different metals, such as aluminum and steel, and in the splash-spray environment of shipboard topside where metal components are always exposed to severe corrosive elements their destructive effect is seriously aggravated at the juncture of these dissimilar metals.
The bonding straps of the prior art are typically constructed of copper cable to optimize electrical conductivity. At each end of the cable is an attached lug of a metal type selected to provide metallurgical compatibility with the metal of the component to which the lug is to be attached. Thus, when the shipboard components to be bonded are of different metal types, the lugs on each end of the strap must be of a different type to match the metal to which they will be mated, creating at least two dissimilar metal interfaces in the bonding strap itself. Because of the difficulty of welding the various metals of the strap construction together by conventional means, the components of the strap are mechanically joined, creating crevices and interstices in which corrosion becomes localized and accelerated. The cable and the cable lug crimped joints are usually encased in a shielding material designed to protect the assembly from the corrosive environment, however, currently available sealing materials break down in the topside environment, exposing the galvanically dissimilar metals in the strap to the sea water environment and consequent accelerated deterioration and failure. Recent studies have confirmed that the mean time between failure for bonding straps of the prior art design is less than five years. These corrosion failures often occur at the crimped joint between the cable and the lug.
It is therefore the primary object of the present invention to provide a bonding strap construction which eliminates the corrosion between the dissimilar metals of a strap intended to bond structural components made of dissimilar metals.
A second object of the invention is to provide a bonding strap which minimizes mechanical interconnections.
A further object of the invention is to provide a system of bonding which contemplates that the unavoidable mechanical connections be constructed of similar metals which are galvanically more noble than their dissimilar metal counterparts.
A still further object of the invention is to provide a bonding strap construction which can utilize materials insensitive to crevice corrosion in seawater environments while at the same time exhibiting adequate electrical characteristics such as high conductivity and low magnetic permeability.
Other and still further objects, features and advantages of the present invention will become apparent in the following detailed description of a preferred form of the invention.